The present invention relates to solid and liquid pharmaceutical preparations containing cilansetron as an active substance, and which further contain a sufficient quantity of physiologically compatible water-soluble acid additive to stabilize the cilansetron against racemization. The invention further relates to the use of these acid additives for the stabilizing of cilansetron against racemization in pharmaceutical preparations.
Cilansetron is the generic designation for R-(-)5,6,9,10-tetrahydro-10-[(2-methyl-imidazol-1-yl) methyl]-4H-pyrido[3.2.1-jk]carbazol-11(8H)-one, which is known from U.S. Pat. No. 4,939,136 (=EP 297,651). The compound can be produced in a known manner according to the methods indicated in this patent or analogous thereto. Furthermore, a method is known from U.S. Pat. No. 5,663,343 (=EP 768,309) for obtaining pure enantiomers of cilansetron. Cilansetron has 5 HT-antagonistic properties and can be used as a pharmaceutically active substance. The use of cilansetron for treating diseases of the lower intestines is known from U.S. Pat. No. 5,438,068 (=EP 601,345).
Cilansetron is an optically active compound. In pharmaceutical preparations, cilansetron can partially racemize over time, in particular in open storage, through environmental influences, so that then in addition to cilansetron its optical isomer can also be present in the pharmaceutical preparations. However, for pharmaceutical preparations it is desirable that the active substance contained therein be present in a largely constant, uniform form.